1. Field of the Invention
This invention relates to a hybrid drive unit provided with a plurality of prime movers as a power source for driving a vehicle, and more particularly, to a control system for a hybrid drive unit, wherein a second prime mover is connected through a transmission to an output member, to which a power is transmitted from a first prime mover.
The present invention relates to the subject matter contained in Japanese Patent Application No. 2003-178163, filed on Jun. 23, 2003, which is expressly incorporated herein by reference.
2. Description of the Related Art
One example of this kind of hybrid drive unit is disclosed in JP-A-2002-225578. In the hybrid drive unit described in this publication, an engine and a first motor generator are connected to each other through a synthesizing/distributing mechanism composed of a single pinion type planetary gear mechanism, an output member is connected to the synthesizing/distributing mechanism in a torque a torque transmittable manner, and a second motor generator is connected through a transmission mechanism to the output member.
According to the hybrid drive unit described in JP-A-2002-225578, therefore, a torque synthesized from an output torque of an engine and a torque of the first motor generator in accordance with a gear ratio of the single pinion type planetary gear mechanism appears on an output shaft, and an engine speed can be controlled by the first motor generator. Therefore, it is possible for the engine to be driven for the optimum fuel consumption thereby to improve a fuel consumption of a vehicle. Moreover, the torque can be applied to the output shaft, by generating an electric power (i.e., regeneration of energy) by the first motor generator so as to drive the second motor generator by the electric power generated, when the engine is being driven at the optimum fuel consumption. Therefore, sufficient driving force can be obtained without deteriorating the fuel consumption. Moreover, the torque outputted by the second motor generator can be raised and transmitted to the output shaft, by having an gear ratio to be set by the transmission greater than “1”. And in case the gear ratio is reduced (e.g., in case the transmission is set in a high speed stage), a speed of the second motor generator can be decreased so that the second motor generator can be changed into a low power type or a small size type.
In Japanese Published Examined Application 47-31773, moreover, there is disclosed the hybrid drive unit, in which a low brake is released and a high brake is applied in case of switching to a high gear stage, and in which the high brake is released and the low brake is applied in case of switching to a low gear stage. Thus, the interchange between the high gear stage and the low gear stage can be achieved by switching a connection of the brakes.
According to the invention disclosed in the aforementioned JP-A-2002-225578, the engine is started by driving the first motor generator connected to the engine through the synthesizing/distributing mechanism. However, since the first motor generator is also connected to the output shaft, it is necessary for the torque not to appear on the output shaft during a startup of the engine, by countervailing the output torque of the first motor generator by driving the second motor generator. Therefore, ordinarily, a gear shift is inhibited during the startup of the engine, and is carried out after the startup of the engine is completed. Moreover, since a shifting preparatory control such as a play reducing of a transmission mechanism is required before executing a shifting operation, a time-lag occurs during the period from an instant when a shifting command is outputted until the instant when the shifting operation is substantially started. Because of this, there arises a problem that a rise of the driving force is delayed at the starting time of driving a vehicle, in case the shifting preparatory control is carried out after the engine is started completely.
According to the invention disclosed in the aforementioned Japanese Published Examined Application 47-31773, moreover, there is a problem such that the shocks occur if a timing of switching between the high brake and the low brake is off.